Industrial controllers are special-purpose computers utilized for controlling industrial processes, manufacturing equipment, and other factory automation, such as data collection or networked systems. In accordance with a control program, the industrial controller, having an associated processor (or processors), measures one or more process variables or inputs reflecting the status of a controlled system, and changes outputs effecting control of such system. The inputs and outputs may be binary, (e.g., on or off), as well as analog inputs and outputs assuming a continuous range of values.
Measured inputs received from such systems and the outputs transmitted by the systems generally pass through one or more input/output (I/O) modules. These I/O modules serve as an electrical interface to the controller and may be located proximate or remote from the controller including remote network interfaces to associated systems. Inputs and outputs may be recorded in an I/O table in processor memory, wherein input values may be asynchronously read from one or more input modules and output values written to the I/O table for subsequent communication to the control system by specialized communications circuitry (e.g., back plane interface, communications module). Output modules may interface directly with one or more control elements, by receiving an output from the I/O table to control a device such as a motor, valve, solenoid, amplifier, and the like.
At the core of the industrial control system, is a logic processor such as a Programmable Logic Controller (PLC) or PC-based controller. Programmable Logic Controllers for instance, are programmed by systems designers to operate manufacturing processes via user-designed logic programs or user programs. The user programs are stored in memory and generally executed by the PLC in a sequential manner although instruction jumping, looping and interrupt routines, for example, are also common. Associated with the user program are a plurality of memory elements or variables that provide dynamics to PLC operations and programs. These variables can be user-defined and can be defined as bits, bytes, words, integers, floating point numbers, timers, counters and/or other data types to name but a few examples.
Transmitting, receiving, and storing Programmable Logic Controller (PLC) data generally involves working with a plurality of various protocols—often times proprietary, when accessing such data across various communications networks. Thus, data transactions often involve developing a communications driver and associated software known as middleware to interact with PLCs across networks such as the Ethernet. As one example, if a remote node were to try and retrieve data from a PLC, a middleware communications product would first have to be loaded on the remote node and a driver would have to be configured for the particular network/PLC protocol being employed before a data transaction could occur. Often times, a third software product would have to be installed before such activities as presenting, storing and manipulating such data could occur. Although this type of transaction may work for one particular type of PLC and one particular protocol, this model often breaks down if different PLCs are involved and/or communicate over different networks from the remote node trying to access/manipulate such data. Thus, trying to maintain and access data from various PLC sources employing many different protocols can be exceedingly time consuming to configure and can lead to considerable expense when installing many different software packages in order to attempt to access PLC data.